Oxidation resistant alloys



Patented May 11, 1948 Jacob Kurtz, Teaneck, N. Tungsten Corporation,poration of Delaware 1., assignor to Callite Union City, N. J., a cor-No Drawing. Application January 13, 1944, Serial No. 518,100

3 Claims. (CI. 7522) The present invention relates to alloys having ahigh resistance to oxidation and to the action of strong alkalinesolvents such as fused alkaline nitrates. The alloy of the invention hasparticular advantages for use in making mounts for diamond dies.

Die mounts for hot drawing of wires must have a high resistance tooxidation. In drawing refractory metals, the drawing temperatures arefrequently high enough to cause oxidation of the mounts at present ingeneral use, to such a degree that the die will be loosened in themount. Such a condition greatly impairs or even totally destroys theusefulness of the die, since the bearing in the die is no longerconcentric in relation to the mount, nor is it any longer truly at rightangles to the faces thereof. The axes of the bearings of the diamond niband of the mount must coincide exactly. A high degree of accuracy inthis respect is necessary and even a slight deviation from axialsymmetry will greatly impair the usefulness and efiiciency of the die.Again, in the drawing of tungsten or molybdenum, it frequently happensthat a piece of wire breaks in the die and must be dissolved out. Forthis purpose, a fused alkaline nitrate is generally used. Such powerfulreactants, however, also tend to cause oxidation and even to dissolvethe mount metals generally employed and consequently to loosen the dienib in the mount with the deleterious efi'ects hereinbefore described.

It is an object of the present invention to provide an alloy suitablefor forming die mounts that will resist the oxidizing effects oftemperatures encountered in hot drawing of refractory metal wires, suchas tungsten or molybdenum wires and wires of other high melting pointmetals.

It is a further object to provide an alloy that will be suitable for usewherever it is necessary to prevent oxidation effects of hightemperatures and of strong alkaline reactants.

Briefly described, the alloy of the invention consists of nickel,copper, chronium and silver :ombined in the proportions and according tothe method hereinafter described. It must first be noted, however, thatchromium, when heat ;reated either by fusion methods or by methods )fpowder metallur y, has a marked tendency to ixidize and, in such case,not to alloy in a true :ense with the other constituents noted. On hecontrary, the chromium oxide forms nodes ,nd these nodes are distributedthrough the mass If alloy of the other constituents in a porphyritictructure. Such a result is highly undesirable.

According to the method of the present invention, the chromium is firstalloyed with nickel to form a nickel chromium alloy. This is eiiected byadding 90% nickel powder to 10% chromium powder, both of about 200 meshor finer. The

metal powders are thoroughly mixed as by ball milling until they arethoroughly commingled. The mixed nickel and chromium powders are thenplaced in a mold and compressed under hydraulic pressure of about 10 to20 tons per square inch. The ingot so formed .is then sintered in ahydrogen atmosphere at a temperature of about 300-400 C. Great care mustbe taken to dry the hydrogen, as water vapor, which is present in nearlyall commercially produced hydrogen, is a very active oxidizing agent andwill cause the chromium to oxidize rapidly and to form the undesirableporphyritic structure above described instead of alloying with thenickel. The hydrogen may be dried by bubbling it through sulphuric acidor by passing it over phosphorus pentoxide.

The nickel and chromium may, however, be heat treated in any suitablenon-oxidizing atmosphere other than hydrogen or the heating may becarried out in a vacum as in a high frequency vacuum furnace.

At the temperatures and under the non-oxidizing conditions mentioned,the nickel and chromium are sintered into a porous rod and arethoroughly difi'used so as to form an alloy having a high resistance tooxidation. This rod is then broken down to powder form by mechanicalmeans such as crushing or hammering. I call this alloy metal A.

A second batch of metal nickel powder and copper powder 30% and alsoabout 200 mesh or finer is thoroughly ball milled for several hours oruntil thorough distribution of the constituent powders is obtained. Icall this metal, B metal.

A third batch of metal is then formed by mixing A and B metals in aboutthe following proportions:

Percent 20% metal A 1 metal B 99 I refer to this metal as metal C.

The final alloy isthen formed by mixing from 75%-96% of powdered metal 0with from 25%- 4% of silver powder.

Assuming that the proportions of metal C consist of 10% of metal A andof metal B, and assuming also that the final metal alloy is to consistof 90% of metal C and 10% silver, the

powders consisting of 1 niium; compressing resulting very satisfactoryalloy will consist of the following:

Percent Nickel 64.8

Copper 24.3

Chromium .9

Silver e ,10.0i The proportions'giv'en are by'weighti In my Patent2,374,942 issued May 1, 1945,,

filed contemporaneously with this application, I have described the useof this metaliforforming mounts for dies. The further treatment of the,powdered metal above for making die mounts or for 'other'purposes';will" be the same. I'he powdered metal is first poured into a mold ofthe desired shapet andlcompressed powders with "compacting the sameunder hydraulic pressure describe'dj whether used" in a hydraulic pressunder a pressure M 20 tons pressure to the square inch. I

The pressed compact is removed from thepres's and givenapresintering'treatment in a furnace in a dry hydrogen atmosphere at atemperature of from 300 to 400 C.'for*about one-half hour. Aiurtherand'final 'sinterin'g is then eifected also in" a dryhyd'rogenatmosphere at a temperature of-from' about 800-900 C. for about ahalfho'ur. Under this treatment thorough-diifusion and alloying ofthe'cons'tituents takes place without any trace of porphyriticcharacteristics andthemetal shrinks toabout'92%"to 80 of the volume ofthe compacted mass.

Instead of chr'omium, zirconium, beryllium or aluminum may besubstituted in'= the same proportion as the chromium without substantialchange either'in'tlie method or inthe characteristics of the finalalloy;

Chromium, zirconium, beryllium and aluminum' have-the same properties inadding resistance to oxidation when combined'with the other constituentsof the alloy and should be alloyed separately with nickel in the sameproportions as hereinabove stated for chromium alone to form thepreliminary alloy. Thorough"diffusionlamd alloying of nickel with thesemetals should be elfected before adding to the other constituents if atrue finalalloy is'to be obtained and a--p'or-' phy'ritic structure isto b'e'prevented'. In any case, however, the proportions given abovefor" the constituents are to b'e'observed, via? 75% to 96% ofm'etalCpowder with from 25% to 4% of silver powder; The proportions oftheconstituents of the "final alloy will'then be within'the rangesoffrom'7'0'.2% t074%"nickel, 0.1% to 2.0% of one or more of 'thegroupconsisting of chromium, zirconium, beryllium or aluminum, and from 29.7%to 24% copper alloyed with silver in the propor tions'of 75% to 96% ofthe 'combin'ed met'alsand 25% to'4'%* silver; orfrom 52.65% to"71.04%nickel, 0.075% to 1.92% chromium, zirconium, beryllium or'aluminum,2'2-.'2'Z5% to 23.04% copperand' 25% to 4%" silver. 7

Having thus described my invention, what-I clainrisz' 1; Method ofmaking analloy that comprises first mixing a batch of finely dividedmetal powders" consisting of 90% nickel and 10% chrothesame underhydraulic combining'from 1%-20% an'd'sh'eat treating the mass socompacted first at a temperature'or 300-400 C. and then raisingsaidternpera'ture to about 800-900 C. and maintaining thattemperatureuntil all said constitu- "entmetals are thoroughly diffused, alloyed andsintered.

'2? Themethod of making an alloy of nickel, chromium, copper and silverthat comprises first separatelyforming an alloy of"90% nickel and 10%.chromium, then combining with a batch consisting -3. The methodof'm'aking'analloy of nickeL chromium, copper and silver that comprisesalloy powder consisting of 90% nickel and-10%" chromium; with from99%-80% said'com'bined powders tofrom 25 Number Name Date 1,519,862 MacyDec. 16 1924" 2,075,444 Koehring Mar. 30, 1937" 2,192,744 Howe Mar. 5,1940 2,205,611 Wasserman June 25 1940 2,289,897 B alke- July 1 4, 1942 2,331,909

' OTHER. REFERENCES Powder Metallurgy, by Wulff, publishedlay AmericanSociety for Metals, Cleveland, Ohio;-

1942. Pages 352-377.

from 1%-20%"- ofisaid' nickel chromium alloy inpow'der 'f'orni of '70nickel'powder and': 30% copp'er'powder, and then adding from 75 96% ofsaid combined metal powderssto fr'omfl hydraulic:

and alloying of the constituent of a nickel chromium of nick'el' andcopper'powders in the proportionsofi% nickel and-30% copper; then addingfrom '75%-96'%*-of %-4% ofsilver powders; compacting'the same underhydraulic I-Iensel Oct} 19," 1943* Certificate of Correction Patent No.2,441,126.

It is hereby certifi the printed specification of the above numberedpatent requiring correction as follows: Column 2, lines 45 to 47inclusive for 7 1 Percent I 20 0 meta A 1 1?20% meta A 80% metal B 99read 9 95, 807 metal B and that the said Letters Patent should be readwith this correc same may conform to the record of the eas tion thereinthat the e in the Patent Ofiice. Signed and sealed this 3rd day ofAugust, A. D. 1948.

THOMAS F. MURPHY,

Assistant Uanwnzlm'mer of Patents.

Certificate of Correction Patent No. 2,441,126.

May 11, 1948. JACOB KURTZ r appears in the printed specification of theabove 'on as follows: Column 2 1' mes 45 to 47 inclusive for 7 l Aercent "I A 20 0 meta 1 17-207 meta metal B 99 read 73-8073 metal B andthat the said Letters Patent should be read with this correction thereinthat the same may conform to e record of the case m the Patent Office.

igned and sealed this 3rd day of August A THOMAS F. MURPHY,

Assistant Uanum'm'oner of Patenta.

